Diabetic foot ulcer presents as open sore in about 15% of diabetics. They are commonly located at the bottom of the foot. Most diabetics’ hospital admission are results of foot ulcer (American Podiatric Medical Association, 2016). Diabetes is a metabolic disorder characterised by hyperglycaemia which results from defects in insulin action, secretion or both. Foot ulcers are complications of uncontrolled diabetes. It could also be due to muscle atrophy, foot deformity, peripheral neuropathy and neuropathic fractures (Raja, 2007).
The prevalence of diabetic foot ulcer is about 13% in North America, 3% in Europe, 7.2% in Africa, 18.1% in Khartoum, Sudan, 15% in Tanzania, 13% in Cameroon and 9.5% in Nigeria (Almobarak et al. 2017).
These result in two thirds of all non-traumatic amputations. Disease presentations include Charcot joint, ulcerations, fracture or gangrene (Krishman et al. 2008; Spichler et al. 2015).
The bacteriology of diabetic foot infection is highly complicated and mostly polymicrobial. It involves both aerobes and anaerobes. Many researchers have presented a picture of mixed infection with aerobic and anaerobic bacteria (Chin, 2013). Some of the aerobic bacteria associated with diabetic foot infection include Staphylococcus aureus, S. saprophyticus, S. epididermis, Streptococcus pyogenes, S. mutans, Pseudomonas aeruginosa, Bacillus subtilis, Proteus species, Escherichia coli and Klebsiella pneumoniae. The anaerobic bacteria include Peptostreptococcus species, Anaerobic Streptococci, Bacteriodes fragilis and Clostridium species (Lipsky et al. 2012; Richard et al. 2012).
Diagnosis is based on combination of signs such as erythema around lesion, local tenderness, local warmth, pus, swelling and indurations. The risk factors are middle or old age, diabetic neuropathy, infection, cigarette smoking, poor glycaemic control, previous foot ulcerations, amputations and ischemia of small and large blood vessels (Scott, 2013; Wu et al. 2007).
Diabetic foot infection can be either superficial or deep. The deep infection involves the muscles, bones, superficial fascia and joints. This includes cellulitis, necrotizing cellulitis and wet gangrene. Once the foot ulcer gets to this stage, the patient is advised on the option of amputation.
The severity of a diabetic foot infection is grouped into four grades depending on their symptoms (Raja, 2007). There are no signs and symptoms in grade 1 wounds. Grade 2 ulcers have lesions on the skin without systemic involvement nor the deep tissues but with any two of the following: erythema > 0.5–2 cm around the ulcer, local indurations, swelling, tenderness, warmth, pain and purulent discharge. Grade 3 ulcers have erythema > 2.0 cm with infection involving structures deeper than the skin and subcutaneous tissues such as osteomyelitis, septic arthritis, or deep abscess. Grade 4 ulcers present with systemic inflammatory respond with at least two of the following signs: temperature > 38 °C, pulse > 90 bpm, PaCO2 < 32 mmHg, leucocytes > 12,000 or < 4000 per mm3 and 10% of immature (band forms) leucocytes (Raja, 2007).
Pal and Gupta (2016) in their study in Kolkata, India, reported that grade 4 foot ulcers on diabetic patients were commonly infected with mixed variety of bacteria including ESBL Klebsiella species, Methicillin-resistant Staphylococcus aureus (MRSA) and so on. They also reported that patients with very long hospital stay had negative culture reports.
In cases where the foot ulcers have developed, infection may be avoided by maintaining good hygiene in and around the foot ulcer and covering the purulent lesions with a waterproof dressing (Singh et al. 2015). Diabetic foot infections are usually inadequately managed due to poor knowledge on the microbial agents associated with the ulcers. There is a need to investigate the pathogens infecting these ulcers and their susceptibility pattern which may improve the patient’s management and reduce the frequency of amputation. This study was carried out to characterise aerobic bacteria associated with the foot ulcers, determine antimicrobial susceptibility pattern of isolates to commonly used antibiotics and assess the severity of the diabetic foot among subjects in the locality.